This invention relates to a timing analyzer for a packet network such as a local area network that allows data to be collected automatically regarding the network use patterns.
In a packet network such as a local area network multiple computers exchange messages via a common network medium such as a fiber optic cable. A wide variety of formats and protocols are used to ensure that messages or packets sent by a sending computer are received by the intended receiving computer. Particularly when a large number of computers are coupled to a single network, it ofteen becomes important to understand the use patterns of the network. In particular, if multiple packets are transmitted at simultaneous or near simultaneous times, so called collisions result. An excessive number of collisions can interfere with efficient operation of the network. Furthermore, noise and other unwanted signals can interfere with the intended reception of packets of data. Additionally, other information such as the average size of data packets, the average gap between adjacent packets, and the fraction of time during with packets are being sent are all relevant in analyzing the operation of a network in a given application.
In the past, logic analyzers and oscilloscopes have been used in an attempt to analyze short time periods of operation of a local area network. This approach allows a short segment of a digital signal, such as the carrier detect signal in a local area network, to be graphically displayed. In this approach the logical state of the signal being displayed is often tested on a periodic basis, and the result of each test is stored. The stored data can then be displayed graphically to allow analysis of the time evolution of the signal for a short time period. This approach is limited by the fact that it is not well-suited for long term monitoring. This is because an extremely large storage capacity would be required if the digital signal were tested and stored on a long term basis.
Another approach is used by commercial traffic monitors for local area networks. Such traffic monitors decode packets of data in order to monitor the transmitted data on the network. This approach suffers from several disadvantages. First, since only decoded data is collected, such monitors ignore noise and data in unexpected protocols. Furthermore, the monitor itself must be programmed to respond to the particular data packet protocol used in the local area network being monitored. Since this approach monitors decoded data it is not well-suited to detect short time interval events on the local area network (such as noise) or timing details regarding collisions between data packets.
Thus, both of the prior art approaches discussed above suffer from particular disadvantages, and the need exists for an improved timing monitor which provides high time resolution, yet which is well-suited to monitor activity on a packet network for extended time periods without requiring excessive memory or other storage capacity.